In the manufacture of electrical machines such as motors, generators and transformers, cores such as rotor cores, stator cores and transformer cores are stamped from metal sheet (electrical or dynamo sheet) and then stacked and pressed together into a package. The round shape of the individual stampings leads to the formation of a large proportion of scrap. Moreover such packages of sheet stampings must be pressed firmly together in order to avoid energy losses and a frequency-dependent humming. For this purpose cast pressure plates are generally needed at the ends of the package, the whole assembly being held together by means of bolts or similar fasteners passing through appropriate holes in the stampings and end plates. All this involves considerable expenditure of manufacturing effort and the use of additional prefabricated parts, in addition to the waste of material already mentioned.
It has also been proposed to form cores for axial flux motors by coiling strip having openings therein to accommodate the field windings, the width of these openings being restricted at the top to 2 mm or less in order to minimise the air gap. It is important to form the punched-out openings so that in the wound coil they are so positioned as to form a slot or passage extending radially of the core. Since the field windings have to be inserted through the narrow gap at the top of the opening it is not possible to employ a simple winding machine, and the field windings are generally wound manually, which is both inaccurate and time-consuming, and therefore costly.